Exceptions: do not rethrow from functions with incompatible exception specifications.

[lcartey]

Description

Per [except.spec], by default if an exception specification is violated, the exception is not rethrown and std::terminate is called. I have therefore modified the ExceptionFlow.qll library to no longer propagate exceptions thrown by noexcept or dynamic specification functions where the exception type isn't listed. This should significant reduce the number of false positives reported by this rule.

Note: this has impacted a number of different queries that used the base exception flow library.

Fixes #159.

Change request type

• Release or process automation (GitHub workflows, internal scripts)
• Internal documentation
• External documentation
• Query files (.ql, .qll, .qls or unit tests)
• External scripts (analysis report or other code shipped as part of a release)

Rules with added or modified queries

• No rules added
• Queries have been added for the following rules:
  • rule number here
• Queries have been modified for the following rules:
  • A15-4-2, ERR55-CPP - reduce false positives for noexcept functions which call other noexcept function which may throw.
  • A15-2-2 - reduce false positives for constructors which call noexcept functions.
  • A15-4-5 - reduce false positives for checked exceptions that are thrown from noexcept functions called by the original function.
  • DCL57-CPP - do not report exceptions thrown from noexcept functions called by deallocation functions or destructors.
  • A15-5-1, M15-3-1 - do not report exceptions thrown from noexcept functions called by special functions.

Release change checklist

A change note (development_handbook.md#change-notes) is required for any pull request which modifies:

• The structure or layout of the release artifacts.
• The evaluation performance (memory, execution time) of an existing query.
• The results of an existing query in any circumstance.

If you are only adding new rule queries, a change note is not required.

Author: Is a change note required?

• Yes
• No

🚨🚨🚨
Reviewer: Confirm that format of shared queries (not the .qll file, the
.ql file that imports it) is valid by running them within VS Code.

• Confirmed

Reviewer: Confirm that either a change note is not required or the change note is required and has been added.

• Confirmed

Query development review checklist

For PRs that add new queries or modify existing queries, the following checklist should be completed by both the author and reviewer:

Author

• Have all the relevant rule package description files been checked in?
• Have you verified that the metadata properties of each new query is set appropriately?
• Do all the unit tests contain both "COMPLIANT" and "NON_COMPLIANT" cases?
• Are the alert messages properly formatted and consistent with the style guide?
• Have you run the queries on OpenPilot and verified that the performance and results are acceptable?
  As a rule of thumb, predicates specific to the query should take no more than 1 minute, and for simple queries be under 10 seconds. If this is not the case, this should be highlighted and agreed in the code review process.
• Does the query have an appropriate level of in-query comments/documentation?
• Have you considered/identified possible edge cases?
• Does the query not reinvent features in the standard library?
• Can the query be simplified further (not golfed!)

Reviewer

• Have all the relevant rule package description files been checked in?
• Have you verified that the metadata properties of each new query is set appropriately?
• Do all the unit tests contain both "COMPLIANT" and "NON_COMPLIANT" cases?
• Are the alert messages properly formatted and consistent with the style guide?
• Have you run the queries on OpenPilot and verified that the performance and results are acceptable?
  As a rule of thumb, predicates specific to the query should take no more than 1 minute, and for simple queries be under 10 seconds. If this is not the case, this should be highlighted and agreed in the code review process.
• Does the query have an appropriate level of in-query comments/documentation?
• Have you considered/identified possible edge cases?
• Does the query not reinvent features in the standard library?
• Can the query be simplified further (not golfed!)

[rvermeulen]

Added a FN test case and suggested a comment change to capture an assumption. Not sure if we want to over approximate and rethrow std::bad_exception if that is part of the dynamic exception specification of a function that throws.

[lcartey]

Thanks for the review! As std::bad_exception is never thrown with the default handler (only via custom handlers), and the handler mechanism is deprecated in C++14, I have opted not to add the additional test cases - let me know if you disagree with that. I have clarified the comment in ExceptionFlow.qll to explain how it works and why we exclude it.

[rvermeulen]

Given that the corner case is no longer possible in new standards it is time to without.